Imaging elements form an image when imagewise exposed to light and/or heat and processed to form the desired final product. The term "imaging element" as used herein includes traditional silver halide photographic elements as well as thermally processable imaging elements. The invention is particularly directed to thermally processable imaging elements, but it is to be understood that the invention also relates to other imaging elements.
Thermally processable imaging elements, including films and papers, for producing images by thermal processing are well known. These elements include photothermographic elements in which an image is formed by imagewise exposure of the element to light followed by development by uniformly heating the element. These elements also include thermographic elements in which an image is formed by imagewise heating the element. Such elements are described in, for example, Research Disclosure, June 1978, Item No. 17029 and U.S. Pat. Nos. 3,080,254, 3,457,075 and 3,933,508.
The aforesaid thermally processable imaging elements are often provided with a transparent or translucent overcoat and/or a transparent or translucent backing, with the overcoat being the outermost layer or layers on the side of the support on which the imaging layer is coated and the backing being the outermost layer or layers on the opposite side of the support. Other layers which are advantageously incorporated in thermally processable imaging elements include subbing layers, interlayers and barrier layers.
To be fully acceptable, a transparent or translucent protective layer (e.g., an overcoat or backing layer) for such imaging elements should: (a) provide resistance to deformation of the layers of the element during thermal processing, (b) prevent or reduce loss of volatile components in the element during thermal processing, (c) reduce or prevent transfer of essential imaging components from one or more of the layers of the element into the overcoat layer during manufacture of the element or during storage of the element prior to imaging and thermal processing, (d) enable satisfactory adhesion of the overcoat to a contiguous layer of the element, (e) be free from cracking and undesired marking, such as abrasion marking, during manufacture, storage, and processing of the element, (f) provide adequate conveyance characteristics during manufacture and processing of the element, (g) not allow blocking, adhering or slippage of the element during manufacture, storage, or processing, (h) not induce undesirable sensitometric effects in the element during manufacture, storage or processing, and (i) control the polarity and magnitude of charge on the surfaces of the element. during manufacture, storage, and processing of the element.
A backing layer also serves several important functions which improve the overall performance of thermally processable imaging elements. For example, a backing layer serves to improve conveyance, to reduce static charge, to provide the desired conductivity, reduce dirt and eliminate formation of Newton Rings.
A typical overcoat for thermally processable imaging elements is an overcoat comprising poly(silicic acid) as described in U.S. Pat. No. 4,741,992, issued May 3, 1988. Advantageously, water-soluble hydroxyl-containing monomers or polymers are incorporated in the overcoat layer together with the poly(silicic acid). The combination of poly(silicic acid) and a water-soluble hydroxyl-containing monomer or polymer that is compatible with the poly(silicic acid) is also useful in a backing layer on the side of the support opposite to the imaging layer as described in U.S. Pat. No. 4,828,971, issued May 9, 1989.
Particularly preferred overcoat and backing layers are described in U.S. Pat. Nos. 5,310,640 and 5,547,821, the entire disclosures of which are incorporated herein by reference.
U.S. Pat. No. 4,828,971 explains the requirements for backing layers in thermally processable imaging elements. It points out that an optimum backing layer must:
(a) provide adequate conveyance characteristics during manufacturing steps, PA1 (b) provide resistance to deformation of the element during thermal processing, PA1 (c) enable satisfactory adhesion of the backing layer to the support of the element without undesired removal during thermal processing, PA1 (d) be free from cracking and undesired marking, such as abrasion marking during manufacture, storage and processing of the element, PA1 (e) reduce static charging effects during manufacture and processing, PA1 (f) reduce dirt, PA1 (g) not provide undesired sensitometric effects in the element during manufacture, storage or processing and PA1 (h) provide desired conductivity. PA1 i) forming a solution of poly(vinyl alcohol) in water; PA1 ii) adding a compound of formula I or formula II to the resulting aqueous medium in an amount sufficient to inhibit agglomeration of matte particles: ##STR2## wherein: R.sub.1, represents a hydrogen atom, a straight or branched chain alkyl group, a cyclic alkyl group, an alkenyl group, an aralkyl group, an aryl group, a heterocyclic group an alkylamido group, an arylamido group, and alkylthioamido group, an arylamido group, an alkyl sulfamido group, an arylsulfamido group and PA1 R.sub.2, and R.sub.3, each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cyclic alkyl group an aryl group, a cyano group, an alkylthio group, an aryl thio group, an alkylsulfoxide group an alkylsulfonyl group or a heterocyclic group; ##STR3## wherein: R.sub.4, is a hydrogen atom, an alkyl group or an alkoxy group; and R.sub.5, R.sub.6 and R.sub.7 each represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a cyano group or a nitro group; PA1 iii) adding matte particles to the aqueous medium; PA1 iv) coating an image recording layer onto one side of a support; and PA1 v) coating the aqueous medium containing the matte particles as an overcoat layer over the image recording layer or as backing layer on the side of the support opposite the image recording layer. PA1 (1) a support; PA1 (2) an image recording layer on one side of the support; PA1 (3) a layer on the same side of the support as the image recording layer or on the opposite side of the support, said layer comprising: PA1 R.sub.2, and R.sub.3, each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cyclic alkyl group an aryl group, a cyano group, an alkylthio group, an aryl thio group, an alkylsulfoxide group an alkylsulfonyl group or a heterocyclic group; ##STR5## wherein: R.sub.4, is a hydrogen atom, an alkyl group or an alkoxy group; and R.sub.5, R.sub.6 and R.sub.7 each represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a cyano group or a nitro group. PA1 (i) an aqueous medium comprising water and dissolved therein poly(vinyl alcohol); and PA1 (ii) polymeric matte particles dispersed in said aqueous medium; wherein the aqueous medium further comprises: (I) PA1 (iii) a compound of formula I or formula II: ##STR6## wherein: R.sub.1, represents a hydrogen atom, a straight or branched chain alkyl group, a cyclic alkyl group, an alkenyl group, an aralkyl group, an aryl group, a heterocyclic group an alkylamido group, an arylamido group, and alkylthioamido group, an arylamido group, an alkyl sulfamido group, an arylsulfamido group and PA1 R.sub.2, and R.sub.3, each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cyclic alkyl group an aryl group, a cyano group, an alkylthio group, an aryl thio group, an alkylsulfoxide group an alkylsulfonyl group or a heterocyclic group; ##STR7## wherein: R.sub.4, is a hydrogen atom, an alkyl group or an alkoxy group; and R.sub.5, R.sub.6 and R.sub.7 each represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a cyano group or a nitro group. PA1 R.sub.2, and R.sub.3, each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cyclic alkyl group an aryl group, a cyano group, an alkylthio group, an aryl thio group, an alkylsulfoxide group an alkylsulfonyl group or a heterocyclic group; ##STR9## wherein: PA1 (1) a support; PA1 (2) a thermographic or photothermographic imaging layer on one side of said support; PA1 (3) a backing layer which is an outermost layer and is located on the side of said support opposite to said imaging layer, said backing layer comprising a binder and matte particles dispersed therein; and PA1 (4) an electroconductive layer which is an inner layer and is located on either side of said support, said electroconductive layer having an internal resistivity of less than or equal to 5.times.10.sup.10 ohms/square. PA1 (1) a support; PA1 (2) a thermographic or photothermographic imaging layer on one side of said support; PA1 (3) a non-electroconductive transparent or translucent overcoat layer which is an outermost layer on the same side of said support as said imaging layer; and PA1 (4) an electroconductive transparent or translucent backing layer which is an outermost layer located on the side of said support opposite to said imaging layer; PA1 said electroconductive backing layer comprising a polymeric binder, matte particles and electrically-conductive metal-containing particles dispersed in said binder in an amount sufficient to provide a surface resistivity of less than or equal to 5.times.10.sup.11 ohms/square. PA1 pulverizing and classification of organic compounds, PA1 emulsion, suspension, and dispersion polymerization of organic monomers, PA1 spray drying of a solution containing organic compounds, and PA1 polymer suspension technique which consists of dissolving an organic material in a water immiscible solvent, dispersing the solution as fine liquid droplets in aqueous solution, and removing the solvent by evaporation or other suitable techniques. The bulk, emulsion, dispersion, and suspension polymerization procedures are well known to those skilled in the polymer art and are taught in such textbook as G. Odian in "Principles of Polymerization", 2nd Ed. Wiley (1981), and W. P. Sorenson and T. W. Campbell in "Preparation Method of Polymer Chemistry", 2nd Ed, Wiley (1968). PA1 I. Saturated and unsaturated hydrocarbons and halogenated hydrocarbons, including alkanes, alkenes, alkyl and alkenyl halides, alkyl and alkenyl aromatic compounds, and halogenated alkyl and alkenyl aromatic compounds, especially those having a logP.sub.calc greater than about 3, PA1 II. alcohols, ethers, and carboxylic acids containing a total of about 10 or more carbon atoms, especially those having a logP.sub.calc greater than about 3, PA1 III. esters of saturated, unsaturated, or aromatic carboxylic acids containing a total of about 10 or more carbon atoms, especially those having a logP.sub.calc greater than about 3, PA1 IV. amides of carboxylic acids having a total of 10 or more carbon atoms, especially those having a logP.sub.calc greater than about 3, PA1 V. esters and amides of phosphorus- and sulfur-containing acids having a logP.sub.calc greater than about 3, and other compounds of similar hydrophobicity. PA1 (1) donor-doped metal oxide, metal oxides containing oxygen deficiencies, and conductive nitrides, carbides, and borides. Specific examples of particularly useful particles include conductive TiO.sub.2, SnO.sub.2, V.sub.2 O.sub.5, Al.sub.2 O.sub.3, ZrO.sub.2, In.sub.2 O.sub.3, ZnO, ZnSb.sub.2 O.sub.6 TiB.sub.2, ZrB.sub.2, NbB.sub.2, TaB.sub.2, CrB.sub.2, MoB, WB, LaB.sub.6, ZrN, TiN, TiC, WC, HfC, HfN, ZrC. Examples of the many patents describing these electrically-conductive particles include U.S. Pat. Nos. 4,275,103, 4,394,441, 4,416,963, 4,418,141, 4,431,764, 4,495,276, 4,571,361, 4,999,276, and 5,122,445; PA1 (2) semiconductive metal salts such as cuprous iodide as described in U.S. Pat. Nos. 3,245,833, 3,428,451 and 5,075,171; PA1 (3) a colloidal gel of vanadium pentoxide as described in U.S. Pat. Nos. 4,203,769, 5,006,451, 5,221,598, and 5,284,714; and PA1 (4) fibrous conductive powders comprising, for example, antimony-doped tin oxide coated onto non-conductive potassium titanate whiskers as described in U.S. Pat. Nos. 4,845,369 and 5,116,666.
With photothermographic elements, it is usually necessary to produce a "duplicate image" of the original photothermographic imaging element for low cost dissemination of the image. The duplication process is typically a "contact printing" process where intimate contact between the photothermographic imaging element and the duplication imaging element is essential. Successful duplication of either continuous rolls or cut sheets is dependent on adequate conveyance of the imaging element through the duplication equipment without the occurrence of slippage or sticking of the protective overcoat layer of the photothermographic imaging element in relation to any of (1) the duplication equipment, (2) the duplication imaging element or (3) the backing layer of subsequent portions of the photothermographic imaging element (adjacent convolutions of the photothermographic imaging element if in a continuous roll or adjacent "cut sheets" in a stacking configuration). These phenomena can include "blocking" and static charge buildup.
The addition of matte particles in the protective overcoat layers is commonly used to prevent adhering or "blocking" between the protective overcoat layer and adjacent backing layer with which it is in intimate contact during manufacture, storage, processing and photo duplication. Furthermore, the matte particles are necessary to impart anti-frictional characteristics to the protective overcoat and/or layer to achieve proper conveyance without sticking, blocking or slippage during the duplication process. The amount and particle size must be carefully controlled as the wrong particle size and/or amount can cause both conveyance, master and duplicate image quality problems.